I guess I need to clarify  things a bit. I have several sets of flare nut wrenches and get no joy from them. The problem is not twisting the lines but  breaking the nut loose without rounding it off. Tried several sets and all the same, they spring open when subjected to the force needed to break the nut loose. The nuts have had a bath in penitrating oil to no avail. Sometimes they warp the nut instead of rounding it off.  I have had sucess with carefully using vice grips but don't like it as it is very easy to mangle the nut. need  some kind of wrench that closes the gap.
mike